Year 9 SQA Science: Formula and Theorem Quick Reference | SQA 九年级科学：公式定理速查手册

📚 Year 9 SQA Science: Formula and Theorem Quick Reference | SQA 九年级科学：公式定理速查手册

This quick-reference handbook brings together the essential formulas and theorems you will meet in Year 9 SQA Science. Use it to revise, practise and build confidence as you link mathematical relationships to the physical, chemical and biological worlds.

本速查手册汇总了九年级 SQA 科学课程中的核心公式与定理。你可以用它来复习、练习，并在将数学关系与物理、化学和生物世界联系起来的过程中建立自信心。

1. Speed and Velocity | 速度与速率

Speed tells you how fast an object is moving, without regard to direction. The formula for average speed is distance travelled divided by time taken.

速度描述物体运动的快慢，不考虑方向。平均速度的公式是移动距离除以所用时间。

v = d / t

Here v is speed (metres per second, m/s), d is distance (m) and t is time (s).

其中 v 代表速度（米每秒，m/s），d 代表距离（m），t 代表时间（s）。

Velocity is a vector quantity: it gives speed in a specific direction. The same formula is used, but the direction matters when combining velocities.

速度是一个矢量：它给出特定方向上的速率大小。同样的公式用于计算速率，但合并速度时必须考虑方向。

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2. Acceleration | 加速度

Acceleration is the rate at which velocity changes with time. It can be a positive increase in speed or a negative deceleration.

加速度是速度随时间变化的快慢。它可以是速度的正向增加（加速），也可以是负向减小（减速）。

a = (v - u) / t

In this relation, a is acceleration (m/s²), v is final velocity (m/s), u is initial velocity (m/s) and t is time (s). The change in velocity Δv equals v - u.

在此关系中，a 是加速度（m/s²），v 是末速度（m/s），u 是初速度（m/s），t 是时间（s）。速度变化量 Δv 等于 v - u。

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3. Newton's Second Law | 牛顿第二定律

An unbalanced force acting on an object causes it to accelerate. The acceleration is proportional to the net force and inversely proportional to the mass of the object.

作用在物体上的非平衡力会使物体产生加速度。加速度与净力的大小成正比，与物体的质量成反比。

F = m a

Here F is the net force in newtons (N), m is mass (kg) and a is acceleration (m/s²). 1 N is the force needed to accelerate 1 kg at 1 m/s².

其中 F 是净力（牛顿，N），m 是质量（kg），a 是加速度（m/s²）。1 N 的大小等于使 1 kg 物体产生 1 m/s² 加速度所需的力。

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4. Weight and Mass | 重量与质量

Weight is the force of gravity acting on a mass. Mass stays the same everywhere, but weight changes with the strength of the gravitational field.

重量是重力作用在物体上的力。质量处处相同，而重量会随引力场强度变化。

W = m g

rength. On Earth g ≈ 9.8 N/kg (often rounded to 10 N/kg). Do not confuse mass with weight.

W 代表重量（N），m 代表质量（kg），g 是引力场强度。在地球表面 g ≈ 9.8 N/kg（常近似为 10 N/kg）。注意不要混淆质量与重量。

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5. Density | 密度

Density is the mass per unit volume of a substance. It helps explain why some materials float while others sink.

密度是物质单位体积的质量。它有助于解释为什么有些材料会漂浮而有些会下沉。

ρ = m / V

ρ (rho) is density (kg/m³ or g/cm³), m is mass (kg or g) and V is volume (m³ or cm³). Water has a density of 1 g/cm³ (1000 kg/m³).

符号 ρ 代表密度（kg/m³ 或 g/cm³），m 是质量（kg 或 g），V 是体积（m³ 或 cm³）。水的密度为 1 g/cm³（1000 kg/m³）。

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6. Pressure | 压强

Pressure is the force applied perpendicular to a surface per unit area. It explains how concentrated forces produce different effects.

压强是垂直作用在单位面积上的力。它解释了集中力为何能产生不同效果。

p = F / A

p is pressure (pascals, Pa), F is force (N) and A is area (m²). 1 Pa = 1 N/m².

p 代表压强（帕斯卡，Pa），F 代表作用力（N），A 代表受力面积（m²）。1 Pa = 1 N/m²。

In fluids the pressure at a given depth also depends on the fluid's density and the gravitational field strength.

在流体中，某一深度的压强还取决于流体的密度和引力场强度。

p = ρ g h

Here h is the depth below the fluid surface (m), ρ is the fluid density (kg/m³) and g is gravitational field strength (N/kg).

其中 h 是液面以下的深度（m），ρ 是流体密度（kg/m³），g 是引力场强度（N/kg）。

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7. Ohm's Law | 欧姆定律

For a metallic conductor at constant temperature, the current flowing through it is directly proportional to the potential difference across it.

对于恒温下的金属导体，通过它的电流与其两端的电势差成正比。

V = I R

urrent (amperes, A) and R is resistance (ohms, Ω). This law can be rewritten as R = V / I.

V 代表电压（伏特，V），I 代表电流（安培，A），R 代表电阻（欧姆，Ω）。此定律可改写为 R = V / I。

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8. Electrical Power and Energy | 电功率与电能

Electrical power is the rate at which electrical energy is transferred by a circuit. The power rating of an appliance helps you estimate energy use.

电功率是电路传输电能的速率。电器的功率额定值有助于估算其用电量。

P = I V

P is power (watts, W), I is current (A) and V is voltage (V). Using Ohm's law, this can also be expressed as P = I² R or P = V² / R.

P 代表功率（瓦特，W），I 代表电流（A），V 代表电压（V）。结合欧姆定律也可表示为 P = I² R 或 P = V² / R。

rgy is measured in joules (J), where 1 J = 1 W s. Larger amounts use kilowatt-hours (kWh).

转移的能量等于功率乘以时间：E = P t。能量的单位是焦耳（J），1 J = 1 W s。较大的能量用千瓦时（kWh）。

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9. Work, Kinetic Energy and Potential Energy | 功、动能与势能

Work is done when a force moves an object through a distance in the direction of the force. Energy is transferred during the process.

力使物体沿力的方向移动一段距离时做功，同时能量发生转移。

W = F d

W is work (J), F is force (N) and d is distance moved in the direction of the force (m).

W 代表功（J），F 代表力（N），d 代表沿力方向移动的距离（m）。

Kinetic energy is the energy an object possesses due to its motion. The formula is:

动能是物体因运动而具有的能量。其公式为：

Eₖ = ½ m v²

Eₖ (kinetic energy, J), m (kg), v (m/s).

Eₖ 表示动能（J），m 表示质量（kg），v 表示速率（m/s）。

Gravitational potential energy is stored when an object is raised against gravity. It is given by:

重力势能是物体克服重力被举高时储存的能量。由下式给出：

Eₚ = m g h

Here h is the change in height (m) and g is gravitational field strength (N/kg). In a closed system, kinetic and potential energy exchanges obey energy conservation.

其中 h 是高度的变化量（m），g 是引力场强度（N/kg）。在封闭系统中，动能与势能的相互转化遵循能量守恒。

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10. Efficiency | 效率

Efficiency describes how much of the total input energy is converted into useful output energy. No real machine is 100% efficient due to waste energy such as heat.

效率描述总输入能量中有多少转化为有用输出能量。由于存在热量等废能，没有实际机器能达到 100% 的效率。

η = (E_useful / E_total) × 100%

η is efficiency (%), E_useful is useful output energy (J) and E_total is total input energy (J). The same ratio can be used with power: η = (P_useful / P_total) × 100%.

η 代表效率（%），E_useful 代表有用输出能量（J），E_total 代表总输入能量（J）。同样的比值可用于功率：η = (P_useful / P_total) × 100%。

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11. Chemical Equations and Conservation of Mass | 化学方程式与质量守恒

In a chemical reaction, atoms are rearranged but the total mass of reactants equals the total mass of products. This is the law of conservation of mass.

在化学反应中，原子重新组合，但反应物的总质量等于生成物的总质量，这就是质量守恒定律。

A balanced chemical equation uses symbols and numbers to show this conservation. For example, the combustion of hydrogen:

配平的化学方程式用符号和数字表示这种守恒。例如氢气的燃烧：

2 H₂ + O₂ → 2 H₂O

There are four hydrogen atoms and two oxygen atoms on each side of the arrow. Never change the formula of a substance; balance only by placing coefficients in front of the formulas.

箭头两边各有四个氢原子和两个氧原子。切勿改变化学式本身，只能在化学式前面添加系数来配平。

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12. Key Biological Theorems: Photosynthesis and Respiration | 生物学关键定理：光合作用与呼吸作用

Photosynthesis is the process by which green plants use light energy to convert carbon dioxide and water into glucose and oxygen. It is the foundation of most food chains.

光合作用是绿色植物利用光能将二氧化碳和水转化为葡萄糖和氧气的过程，是大多数食物链的基础。

6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂

This word-equation summary represents a series of light-dependent and light-independent reactions occurring in chloroplasts. Light energy is captured by chlorophyll.

这个文字方程式概括了在叶绿体中发生的一系列光依赖与光非依赖反应。光能由叶绿素捕获。

Aerobic respiration releases energy for cells by breaking down glucose using oxygen. The overall equation is essentially the reverse of photosynthesis:

有氧呼吸通过氧气分解葡萄糖为细胞释放能量。其总方程式基本上是光合作用的逆反应：

C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O + energy

This energy is stored as ATP and used for movement, growth and all life processes. Respiration and photosynthesis form a critical carbon cycle.

释放的能量以 ATP 形式储存，用于运动、生长及一切生命活动。呼吸作用与光合作用共同构成关键的碳循环。

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